1. Field of the Invention
The present invention relates to vaporless liquid storage devices, and more specifically, to volatile liquid storage devices which prevent the accumulation of vapor caused by the evaporation of the stored liquid.
2. Description of the Prior Art
The storage of liquids especially volatile liquid often presents problems because of the possible effect of vapor creation, accumulation and release. In the petroleum and chemical industries, liquids such as benzene, crude oil and alcohol need to be stored in a vessel where potentially volatile vapors are not created or accumulated in the vessel.
Liquid storage vessels for storing volatile and other liquids are well known in the art. One type of liquid storage system includes a hard shelled vessel for containing the stored liquid. U.S. Pat. No. 2,863,297 issued to Johnston is of this type. This patent illustrates an apparatus for storing volatile liquids at atmospheric pressure whereby the storage temperature of the liquid is controlled by a radiation shield. U.S. Pat. No. 2,955,723 issued to McGrath also illustrates a closed tank storage system. This system maintains a substantial pressure within the vessel and provides an upper gas storage portion to contain the vapors of the liquid.
Other liquid storage vessels are directed at maintaining the liquid at a desired temperature and/or pressure such as U.S. Pat. No. 3,919,855 issued to Turner. Other prior art devices for containing volatile liquids include vessels with fixed covers and vessels with slidable or floating covers which move upwardly and downwardly as liquid is supplied to or withdrawn from the vessel. These systems do not effectively contain or prevent creation of hazardous vapors from the stored liquid.
Various membrane systems have been developed for storing liquids. U.S. Pat. No. 4,308,973 issued to Irland illustrates a single membrane aerosol container system. Aerosol containers commonly have only one membrane or pouch and do not provide for supply as well as withdrawal of the contained liquid. Another membrane type storage device is depicted in U.S. Pat. No. 2,758,747 issued to Stevens. In that invention, a tank is fitted with one or two flexible bag-type members for the storage of one or two different liquids. The collapsing action of the bag-type member prevents vapor losses of the liquids yet it does not prevent vapor creation.
Another membrane system for storing liquids is illustrated in U.S. Pat. No. 4,836,409 issued to Lane. A hydropneumatic tank is fitted with a diaphragm-liner. One side of the diaphragm-liner contains a compressed gas while the other side contains a liquid. The pressurized gas forces the liquid into and out of the tank as needed. Various other single membrane systems have been used to store liquids in the prior art.
In the storage of gases, a duel membrane system forming two chambers is disclosed in U.S. Pat. No. 4,902,304 issued to Hallen and assigned to the assignee of the present invention. The structure of Hallen includes an inner gas filled chamber connected to a source of gas. A predetermined level of pressure is maintained upon the inner gas storage chamber by an outer membrane which creates an outer air filled chamber. The volume of air within the outer air filled chamber compensates for changes in the volume of gas in the inner chamber to maintain a constant pressure thereon.